Disposable test sensor with improved sampling entrance

ABSTRACT

A disposable electrochemical test sensor designed to facilitate sampling of fluid samples. It has a fluid chamber having a novel extra wide sampling entrance, but no additional air escape vent. The chamber provides a reservoir from which a sample fluid can be drawn into the chamber through capillary action. The sampling entrance provided can draw fluid into the chamber through any part of the opening, allowing easy targeting the samples with small volume, picking up smeared samples, and added tolerance to users who jam the tip of the sensor into users&#39; finger. The sampling entrance also serves as air escape vent. Such one opening sensor alleviates over-flow issue often encountered in convenient sensors.

FIELD OF THE INVENTION

The present invention generally relates to a test sensor or strip. Morespecifically, the present invention generally relates to a disposablebiosensor with a fluid chamber that is adapted to receive a fluid samplearound with small volume. Still more specifically, the present inventiongenerally relates an electrochemical biosensor with an extra widesampling entrance. Still more specifically, the present inventionrelates methods of making and using the biosensors.

BACKGROUND OF THE INVENTION

The use of disposable test sensors such as strips in the medical fieldfor testing various analytes in body fluid is well known. The accuratedetermination of analytes in body fluids is of great importance in thediagnoses of certain physiological abnormalities. In particular, it isimportant that diabetic individuals frequently check their glucose levelin their body fluids to regulate the glucose intake in their dailydiets. The results of such tests can be used to determine the insulindosage or other medication needs to be administered. In one type ofblood-glucose testing system, test sensors, or called glucose strips,are used by diabetic individuals to test a sample of blood in connectionwith a hand-held meter. The glucose strips are used by millions ofdiabetics throughout the world on a daily base.

There are hundreds of brand names of glucose strips in the market. Theyare very similar in terms of sensor construction: i.e., a channel isformed between a generally U-shaped spacer and is adapted to receiveblood from the opening end of the sensor through capillary action andescape air from the other end through an air escape vent. In order toreduce blood volume, thus reduce pain from piercing finger or othersampling points, the blood receiving chamber is usually small and, as aresult, the sampling entrance is also relatively small. As the volume offluid chambers in the sensors decreases, it becomes increasingly moredifficult to fill the fluid chamber with the sample to be analyzed. Ithas been observed that users may abuse the test sensor by jamming thetip of the test sensor into the individual's finger, which very probablyresults in incomplete blood filling, non-continuous filling or wigglingof blood flow. Additionally, in some existing test sensors, it isdifficult to position the fluid sample within the channel entranceopening especially for those diabetics who have poor vision and/ortrembling hand. Besides, blood samples turn to smear around the tip offingers or other sampling points. It becomes very difficult to draw suchsmeared blood into the sensor chamber. All of these phenomena mayeventually lead to biased readings, and as a result, wrong dosage ofinsulin administration and even life threatening errors may occur.

Therefore, in order to reduce or eliminate such biased readings causedby such user action and/or reduce the difficulty in connection withsampling, it would be highly desirable to have a more user friendly testsensor that could easily target sample, easily draw sample into thesensor chamber, and alleviate incomplete filling, non-continuous fillingand other issues that may result in inaccurate test results. The presentdisclosure is directed to a novel design and method to overcome one ormore of the limitations in the prior arts.

SUMMARY OF THE INVENTION

According to the first embodiment, a disposable electrochemical testsensor has a sample chamber having a novel extra wide sampling entrance,but no additional air escape vent. Such a design is adapted to improvesampling of fluid samples. The fluid chamber provides a reservoir fromwhich sample fluid can be drawn into the sample receiving chamberthrough capillary action. The extra wide sampling entrance provided bythe present invention can draw blood into the chamber through any partof the opening end. Thus it allows easily targeting the samples withsmall volume, picking up smeared samples and alleviating jamming theopening end. The extra wide sampling entrance provided by the presentinvention also serves as the air escape vent. Such one opening sensoreliminates over-flow issue often encountered in convenient sensors. Inpreferred embodiments, the sensor consists of multiple layers whichinclude a base layer having conductive coatings serving as working andreference electrodes; a second base layer used to define the electrodeareas and hold chemistries; a first upper layer having semi-circularshape serving as spacer; and a second upper layer with a hydrophilicsurface facing to the chamber. The upper and base layers are attachedthrough adhesives or other ways to bond each other, such that the fluidchamber is formed between a portion of the lower layer surface and theupper layer surface at one end of the sensor, while the other end of thesensor having conductive layer exposed serve as electric contacts inconnection with a monitor or meter.

According to the second embodiment, a disposable electrochemical testsensor has a sample chamber having a novel extra wide sampling entrance,but no additional air escape vent. Such a design is adapted to improvesampling of fluid samples. The chamber provides a reservoir from whichsample fluid can be drawn into the sample receiving chamber throughcapillary action. The extra wide sampling entrance provided by thepresent invention can draw blood into the fluid chamber through any partof the front opening end, and can also draw blood into the fluid chamberthrough part of left side and part of right side near the opening end.The front opening and both side openings form a large opening, servingas blood sample entrance. Thus such unique design allows easilytargeting the samples with small volume, picking up smeared samples andalleviating jamming of the opening by users' finger. The extra widesampling entrance provided by the present invention also serves as theair escape vent. That is to say the air escape vent joins to the bloodsampling entrance opening. Such two-in-one opening sensor eliminatesover-flow issue often encountered in convenient sensors.

In preferred embodiments, the test sensor consists of multiple layerswhich include a base layer having conductive coatings serving as workingand reference electrodes; a second base layer used to define theelectrode areas and hold chemistries; a first upper layer havingsemi-circular shape serving as spacer; and a second upper layer with ahydrophilic surface facing to the chamber. The upper and base layers areattached through adhesives or other ways to bond each other, such thatthe fluid chamber is formed between a portion of the lower layer surfaceand the upper layer surface at one end of the sensor, while the otherend of the sensor having conductive layers exposed serve as electriccontacts in connection with a monitor or meter.

According to one method, an analyte concentration is measured. Adisposable electrochemical test sensor is provided having a samplechamber having a novel extra wide sampling entrance, but no additionalair escape vent. The chamber provides a reservoir from which samplefluid can be drawn into the sample receiving chamber through capillaryaction. The extra wide sampling entrance provided by the presentinvention also serves as the air escape vent. In preferred embodiments,the sensor consists of multiple layers which include a base layer havingconductive coatings serving as working and reference electrodes; asecond base layer used to define the electrode areas and holdchemistries; a first upper layer serves as spacer which may havedifferent shapes, such as circular arc, square, rectangular, triangle,regular trapezoid, inverted trapezoid; and a second upper layer with ahydrophilic surface facing to the chamber. The upper and base layers areattached through adhesives or other ways to bond each other, such thatthe fluid chamber is formed between a portion of the lower layer surfaceand the upper layer surface at one end of the sensor, while the otherend of the sensor having conductive layers exposed serve as electriccontacts in connection with a monitor or meter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the test sensor of the presentinvention.

FIG. 2 is an exploded view of the test sensor of the present inventionshowing the four component layers.

FIG. 3 is a top view of the test sensor of the present inventionconsisting of four laminated layers according to one embodiment.

FIG. 4 is a top view of a first base layer to be used in forming a testsensor according to one embodiment.

FIG. 5 is a top view of the second base layer to be used in forming atest sensor according to one embodiment.

FIG. 6a is a top view of the first upper layer to be used in forming atest sensor according to the first embodiment.

FIG. 6b is a top view of the first upper layer to be used in forming atest sensor according to the second embodiment.

FIG. 7 is a top view of the second upper layer to be used in forming atest sensor according to one embodiment.

FIG. 8 is a side view of the test sensor according to the firstembodiment of the present invention.

FIG. 9 is a side view of the test sensor according to the secondembodiment of the present invention.

FIGS. 10a, 10b illustrate blood entering the fluid chamber and airescape for the test sensor according to the first embodiment of thepresent invention. Solid arrows and blank arrows denote blood samplingdirections and air escape directions, respectively.

FIGS. 11a, 11b, 11c illustrate blood entering the fluid chamber and airescape for the test sensor according to the second embodiment of thepresent invention. Solid arrows and blank arrows denote blood samplingdirections and air escape directions, respectively.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The test sensor of the present invention is directed to improve samplingentrance of the strip for the determination of an analyte concentrationof in a fluid sample, such as blood. In one embodiment, a test sensor isadapted to receive a fluid sample from one end of the sensor, while theother end is connected with an instrument or meter. Analytes that may bemeasured include, but not limited to glucose, lactate, uric acid,creatinine, creatine, cholesterol, triglycerides, hemoglobin, bilirubin,alcohol, etc. The fluid sample may be any body fluid, thus, the analytesmay be in, for example, a whole blood sample, a blood serum sample, ablood plasma sample, other body fluids like tears, interstitial fluidand urine. In one preferred method, the testing equipment is a hand-heldmeter.

In a particular embodiment, the sensor comprises multiple layers whichinclude a base layer having conductive coatings serving as working andreference electrodes; a second base layer used to define the electrodeareas and hold chemistries; a first upper layer having semi-circularshape serving as a spacer; and a second upper layer with a hydrophilicsurface facing to the chamber. The upper and base layers are attachedsuch that the fluid chamber is formed between a portion of the lowerlayer surface and the upper layer surface at one end of the sensor,while the other end of the sensor having conductive layers exposedserves as electric contacts.

In one embodiment, the test sensor is an electrochemical test sensor.FIG. 1 shows a perspective view of the test sensor of the presentinvention. The sensor has a sensor body 100, an electric contact end 10and sampling end 20. The electric contact end may have at least twocontacts used for one working electrode and one reference electrode,respectively. In one preferred embodiment, the electric contact end hasthree electric contacts serving as contacts for a first workingelectrode 11; a second working electrode 13 and a reference electrode12, respectively. In one embodiment, the test sensor consists ofmultiple layers which include a first base layer 200; a second baselayer 300; a first upper layer 400; and a second upper layer 500, asshown in FIG. 2. FIG. 3 shows a top view of the test sensor consistingof four laminated layers according to one embodiment.

FIG. 4 shows a top view of a first base layer 200 to be used in forminga test sensor according to one embodiment. The first base layer 200 maybe made from a variety of materials such as polymeric materials, coatedwith conductive materials such as carbon, various metals or metaloxides. The first base layer 200 with conductive coating serves assubstrate of the test sensor and chamber forming layer. It also servesas electrodes at one end 20 and electric contacts at the other end 10.Non-limiting examples of polymeric materials, that may be used to formthe base layer include, but not limited to polyethylene, polypropylene,polystyrene, polyvinyl chloride, and polytetrafluoroethylene,polycarbonate, polyethylene terephthalate, polyethylene naphthalate,polyimide and combinations thereof. The conductive coating may be formedby a variety of methods which are well known in the field including, butnot limited to printing (e.g., screen-printing), coating (e.g., reverseroll), vapor deposition, sputtering, chemical deposition, andelectrochemical deposition. The conductive coating may be on a wholepiece of insulating material. If so, a desired number of electricconduits must be made. This can be achieved by etching/scribing therequired number of conductive conduits. The etching process may beaccomplished chemically, by mechanically scribing lines in theconductive layer, or by using a laser to scribe the conductive layerinto separate conductive conduits. The conductive materials may be, butnot limited to various carbon materials; various noble metals like gold,platinum, palladium, iridium, rhodium, ruthenium; various metal oxideslike indium oxide, tin oxide; and combinations thereof.

FIG. 5 shows a top view of the second base layer to be used in forming atest sensor according to one embodiment. The second base layer 300virtually has same width as the first base layer 200, but shorter inlength at the end 10 to expose electric contacts. The second base layer300 is made of electric insulating layer and it is shorter than thefirst base layer at the electric contact end 10 so that conductivecoating at the first base layer can be exposed for electric contactswhen connected with test monitoring device like a hand-held meter. Thesecond base layer 300 has at least one cutout at the end 20. The cutoutexposes a part of the conductive layer when laminated with the firstbase layer 200 and thus defines the electrode area. The cutout can alsohold chemistries within the well formed. In one embodiment, the secondbase layer 300 has at least two such cutouts. In one preferredembodiment, the second base layer 300 has three round cutouts (31, 32,33) at the end 20 serving as a first working electrode 31; a referenceelectrode 32 and a second working electrode 33. These cutouts have adiameter ranging from 0.1 mm to 2.5 mm. Preferably, the diameter isranging from 0.5 mm to 1.5 mm. More preferably, it is around 1 mm. Theelectrode cutouts 31, 32, 33 have a certain depth, which depends on thethickness of the electric insulating materials used, thus form threewells and can hold chemistries within the wells. Preferably, thethickness of the electric insulating materials is from 0.01 mm to 0.2mm. More preferably it is around 0.05 mm. In one embodiment of thepresent invention, the electrode cutouts 31, 32, 33 in the second baselayer 300 have the same shape and dimensions. But they can havedifferent shapes, dimensions and/or arrangement orders, withoutdeviating from the scope and spirit of the present invention. Theplacement of all of the cutouts is such that they will be all positionedwithin the sample fluid chamber described above. The cutouts may be madeby die cutting the insulating material mechanically, or cutting with alaser, and then fastening the material to the first base layer. Anadhesive, such as a pressure-sensitive adhesive, may be used to securethe second base insulating layer 300 to the first base layer 200.Adhesion may also be accomplished by ultrasonically bonding the secondbase layer 300 to the first base layer 200. The second base layer 300may also be made by screen printing an insulating material, by binding aphotopolymer or by heat-sealing an insulating material over the firstbase layer 200.

FIG. 6a shows a top view of the first upper layer 400 a to be used informing a test sensor according to the first embodiment. The first upperlayer 400 a virtually has same width and length as the second base layer300. The first upper layer 400 a serves as a spacer in between the twobase layers 200/300 and the second upper layer 500. The first upperlayer 400 a, or spacer, is also made of a plastic insulating materialwith glue or adhesive on both sides and creates the sample fluid chamberof the laminated body (FIGS. 1-3). It contains a semi-circular shapedcutout 41 a at the end 20 which overlays the second base layer 300 withthe open end corresponding to the open end of the laminated bodydescribed earlier. The semi-circular shaped cutout 41 a has a diameterof at least 1 mm. The diameter can be larger than or equal to the widthof the first base layer 200 or second base layer 300. Preferably, it isslightly smaller than the width of the second base layer 300. Morepreferably, it is around 2 mm to 20 mm in the present invention.Assuming the test sensor or the component layers (200, 300, 400 a and500) in the present invention have a width of around 6 mm, preferably,the diameter of the semi-circular shaped cutout is around 5.2 mm. Thus,a blood sample can enter the fluid chamber from any part of the entireopening end. A double coated, pressure-sensitive adhesive tape may beused as the first upper layer 400 a. The cutout 41 a creating the fluidchamber may have different shapes, including, but not limited tosemi-circular, circular arc, square, rectangular, triangle, regulartrapezoid, inverted trapezoid and etc. In one preferred embodiment, thecutout is in semi-circular shape. Obviously, the thickness and size ofthe cutout 41 a determine the volume of the capillary chamber.Preferably, the first upper layer 400 a has a thickness ranging from0.01 mm to 0.5 mm, thus, the volume of the fluid chamber is about 0.1 to5 microliter in the present invention.

FIG. 6b shows a top view of the first upper layer 400 b to be used informing a test sensor according to the second embodiment. The firstupper layer 400 b is alternative to the first upper layer 400 a. Thefirst upper layer 400 b also serves as a spacer in between the two baselayers 200/300 and the second upper layer 500. The first upper layer 400b virtually has same width as the first upper layer 400 a, but it isslightly shorter in length at the end 20, as a result, leaving openingsat both corners after all four component layers 200, 300, 400 b and 500are laminated. Such a unique design of the present invention forms anover 180° sampling entrance, even wider opening compared to the firstembodiment described above. Therefore, a blood sample not only entersthe fluid chamber from any part of the front opening, but also from bothside opening of the test sensor at the end 20. The first upper layer 400b, or spacer, is also made of a plastic insulating material with glue oradhesive on both sides and creates the sample fluid chamber of thelaminated body. It contains a semi-circular shaped cutout 41 b on theend 20 which overlays the second base layer 300 with the open endcorresponding to the open end of the laminated body described earlier.The semi-circular shaped cutout 41 b has a diameter of at least 1 mm.The diameter can be larger than or equal to the width of the second baselayer 300. Preferably, it is slightly smaller than the width of thesecond base layer 300. More preferably, it is around 2 mm to 20 mm.Assuming the test sensor or the component layers (200, 300, 400 a and500) in the present invention has a width of around 6 mm, preferably,the diameter of the semi-circular shaped cutout is around 5.2 mm. Adouble coated, pressure-sensitive adhesive tape may be used as the firstupper layer 400 b. The cutout 41 b creating the fluid chamber may havedifferent shapes, including, but not limited to semi-circular, circulararc, square, rectangular, triangle, regular trapezoid, invertedtrapezoid and etc. In one preferred embodiment, the cutout is insemi-circular shape. Obviously, the thickness and size of the cutout 41b determine the volume of the capillary chamber. Preferably, the firstupper layer 400 b has a thickness ranging from 0.01 mm to 0.5 mm, thus,the volume of the fluid chamber is about 0.1 to 5 microliter in thepresent invention.

The laminated body may also have a second upper layer 500, as shown inFIG. 7, bonded to the first upper layer 400 a or 400 b, but without anadditional vent opening, which is needed in convenient sensors. Itvirtually has the same width and length as the second base layer 300 orfirst base layer 400 a in the first embodiment. While in the secondembodiment, the second upper layer 500 may have the same width andlength as the second base layer 300, thus, it is slightly longer thanthe first base layer 400 b, such that side opening creates at the end20. Still in the second embodiment, the second upper layer 500 may havethe same width as the second base layer 300, but it can also have alength equal to or larger than the first upper layer 400 b. The secondupper layer 500 is made of a plastic or polymer materials. Non-limitingexamples of polymeric materials, that may be used to form the secondupper layer 500, include, but not limited to polyethylene, polyethyleneterephthalate, polyethylene naphthalate, polyimide and combinationsthereof. In one embodiment, the second upper layer 500 has a hydrophilicsurface facing to the chamber to facilitate the capillary action. Itshould be understood that the entire side of the second upper layer 500may be coated with a hydrophilic substance and then bonded to the firstupper layer 400 a or 400 b. In the present invention, it is not criticalto have an additional vent opening at the second upper layer 500.

Because of the unique design of the extra wide sampling entrance in thepresent invention, air escape is not an issue when a fluid sample suchas blood enter the fluid chamber. Air can always find a way to escapefrom some part of the wide opening. Convenient test sensors alwayscontain a vent opening for air escape when a fluid sample enterscapillary channels. However, such vent opening may often cause problems,such as overflow, that may generate erratic test results. Besides, usersmay accidently apply blood sample to the vent opening instead of thenormal blood sampling entrance, that may also compromise the testresults. The test sensor of the present invention with combination ofsampling entrance and air escape vent in one extra wide openingvirtually eliminates such issues.

FIG. 8 shows side view of the test sensor of the first embodimentconsisting of four laminated layers including a first base layer 200,second base layer 300, first upper layer 400 a and second upper layer500.

FIG. 9 shows side view of the test sensor of the second embodimentconsisting of four laminated layers including a first base layer 200,second base layer 300, first upper layer 400 b and second upper layer500. Note 91 denotes the side opening described earlier. Obviously, itsthickness is the same as the first upper layer 400. The length of theside opening 91 is preferably from 0.01 mm to 2.5 mm. More preferably,it is from 0.1 to 0.3 mm. Still more preferably, it is around 0.25 mm.It should be emphasized that the side opening 91 in the unique design ofthe present invention is just a part of the extra wide sampling opening.The side and front opening combine to form an over 180° sampling angle.

The advantage of the test sensor for blood sampling and air escape canbe illustrated through FIGS. 10 and 11.

FIGS. 10a, 10b illustrate blood entering the fluid chamber and airescape for the test sensor according to the first embodiment of thepresent invention. Note solid arrows and blank arrows denote bloodsampling directions and air escape directions, respectively. Because ofthe extra wide sampling entrance opening of the present invention, bloodsample can enter the fluid chamber from any part of the front opening,while air escapes from the rest of the opening. For example, if bloodsample enters from the middle of the opening, air can escape from bothside of the front opening (FIG. 10a ); if blood sample enters from oneside of the front opening, air can escape from the other side (FIG. 10b).

FIGS. 11a, 11b, 11c illustrate blood entering the fluid chamber and airescape for the test sensor according to the second embodiment of thepresent invention. Note solid arrows and blank arrows denote bloodsampling directions and air escape directions, respectively. Because ofthe extra wide sampling entrance opening of the present invention, bloodsample can enter the fluid chamber from any part of the over 180°opening, while air escapes from the rest of the opening. For example, ifblood sample enters from the middle of the front opening, air can escapefrom both side of the front opening as well as from the side opening 91(FIG. 11a ); if blood sample enters from one side of the front opening,air can escape from the other side of the front opening as well as fromthe side opening 91 (FIG. 11b ); if blood sample enters from one sideopening 91, air can escape from the front opening as well as from theother side opening 91 (FIG. 11c ).

Obviously, by having a test sensor with the extra wide openings in thefirst embodiment or second embodiment, being adapted to receive a fluidsample, the test sensor of the present invention more easily receivesthe fluid sample from a user and is more tolerant to users who jam thetip of the sensor into his/her finger, is more tolerant to fluid sampleswith very small volume (less than 1 microliter) and even smeared sampleson the finger tip.

Referring back to FIGS. 1-3, the electrode cutouts 31, 32, 33 may beloaded with chemistries that react with an analyte to produce detectableelectrochemical signals. The chemistries may contain an enzyme, anantibody, an antigen, a complexing reagent, a substrate or combinationthereof. The reagents are selected to react with the desired analyte oranalytes to be tested so as to assist in determining an analyteconcentration of a fluid sample. In one embodiment, the reagentstypically contain an enzyme such as, for example, glucose oxidase,glucose dehydrogenase, cholesterol oxidase, creatinine amidinohydrolase,lactate oxidase, peroxidase, uricase, xanthine oxidase and etc. whichreacts with the analyte and with an electron acceptor such as aferricyanide salt to produce an electrochemically measurable speciesthat can be detected by the electrodes. For example, if the analyte ofthe test sensor is glucose, then glucose oxidase or glucosedehydrogenase may be included as the enzyme; if the analyte of the testsensor is uric acid, then uricase may be included as the enzyme. Itshould be noted that in some cases more than one enzyme may be includedto construct the test sensor in order to generate detectableelectrochemical signal. For example, in order to make a test sensor forcholesterol, cholesterol esterase, cholesterol oxidase and peroxidasemay be included in the sensor.

In order for the test sensor works effectively, the electrode cutouts31, 32, 33 may comprise a mixture of a polymer, an enzyme, a surfactant,an electron acceptor, an electron donor, a buffer, a stabilizer and abinder. The electrode cutouts 31, 32, 33 may further include a mediatorthat is an electron acceptor and assists in generating a current thatcorresponds to the analyte concentration. The preferable mediators couldbe redox chemicals either in oxidized or reduced form. The mediator usedin the present invention may include, but not limited to various metalor noble metal complexes such as potassium ferricyanide, potassiumferrocyanide, cobalt phthalocyanine, various ferrocenes, and variousorganic redox mediators such as methylene blue, methylene green,7,7,8,8-tetracyanoquinodimethane, tetrathiafulvalene, toluidine blue,meldola blue, N-methylphenazine methosulfate, phenyldiamines,3,3′,5,5′-tetramethylbenzidine, pyrogallol, and benzoquinone,phenanthroline-5,6-dione and etc. For example, if the enzyme used toconstruct the test sensor is glucose oxidase or glucose dehydrogenase,then potassium ferricyanide may be included as redox mediator; if theenzyme used to construct the test sensor includes peroxidase, thenpotassium ferrocyanide may be included as redox mediator.

The electrode cutouts 31, 32, 33 include a first working electrode 31, asecond working electrode 33 and a reference electrode 32. In oneembodiment, the second working electrode 33 serves as a blank electrodewithout loading a chemistry that reacts with the analyte, such thatbackground signal can be measured and be subtracted from the analytesignal resulted from the first working electrode 31. In this embodiment,effect of interference substances on the analyte signal could beminimized. Still in this embodiment, the electric signals such ascurrent, impedance at the working electrodes 31 and 33, and time toobtain these signals could be used to estimate filling status of thefluid chamber (filled or not). Thus, this embodiment could alertunder-fill of fluid samples.

Although the description of test sensor construction above describesconstruction for a single sensor, the design and materials used can alsobe used for making multiple sensors from one large piece of each layermaterial. This would be accomplished by starting with relative largepieces of the first base layer material, second base material, firstupper layer material and second upper layer material. After a series ofpreparations described above, a plurality of multiple test sensors thuscan be constructed to achieve mass production in a cost-effective way.

It should be noted that although the particular embodiments of thepresent invention have been described herein, the above description ismerely for illustration purpose. Further modification and variations ofthe invention herein disclosed will occur to those skilled in therespective arts and all such modifications and variations are deemed tobe within the scope of the invention as defined by the appended claims.

What is claimed is:
 1. A sensor for sampling fluid samples comprising: abase layer, comprising three sampling wells at a front end, the threesampling wells in electric communication with an electric contact end ofthe base layer; a spacer attached to the base layer having a recessedportion on a front edge defining a fluid cavity, the fluid cavityconstructed and arranged to be in fluid communication with the first,second, and third sampling well of the base layer; and wherein the threesampling wells are arranged to define an approximate triangle, the firstwell positioned at a vertex angle opposite to the triangle base which isdefined by the second and third wells, the first well being farther froma front edge of the base layer than the second and third wells, thesampling well arrangement providing accurate current so long as a fluidis contacting at least two of the three sampling wells.
 2. The sensor ofclaim 1 further comprising an upper layer, the upper layer positionedabove the spacer and defining a top of the fluid cavity, a fluid inletformed along a front edge of the spacer providing fluid access to thefluid cavity and defined by front edges of the base layer and the upperlayer.
 3. The sensor of claim 1 wherein the base layer is formed of afirst base layer, and a second base layer, the second base layerdefining the first, second, and third sampling wells by forming anaperture through its thickness.
 4. The sensor of claim 2 wherein theshape and dimensions of the fluid cavity facilitate the drawing of afluid sample into the fluid cavity using a capillary action.
 5. Thesensor of claim 4 wherein the fluid inlet serves as an air escape ventto facilitate the fluid sample being drawn into the fluid cavity usingthe capillary action.
 6. The sensor of claim 1 wherein the recessedportion of the spacer forms a semi-circular cross section of the fluidcavity.
 7. The sensor of claim 1 wherein the first, second, and thirdsampling well serve to hold a chemical selected to react with an analytein a fluid sample to produce an electrochemical signal.
 8. The sensor ofclaim 7 wherein the chemical is formed from substrates selected from thegroup consisting of: enzymes, antibodies, complexing reagents andcombinations thereof.
 9. The sensor of claim 7 wherein the chemical isformed from a mixture of a polymer, an enzyme, a surfactant, an electronacceptor, an electron donor, a buffer, a stabilizer and a binder. 10.The sensor of claim 7 wherein the chemical further comprises a mediatorthat is an electron acceptor, the mediator being redox chemicals eitherin oxidized or reduced form.
 11. The sensor of claim 2 wherein thespacer is an electrically insulating material.
 12. The sensor of claim 2wherein the bottom surface of the upper layer is a hydrophilic surface.13. The sensor of claim 1 wherein the recessed portion of the spacer iscentrally disposed along the front edge of the spacer.
 14. The sensor ofclaim 2 wherein the spacer is a double-sided adhesive tape.
 15. Thesensor of claim 2 wherein the front sampling end of the spacer isrecessed from the front edge of the upper layer front sampling end andrecessed from the front edge of the base layer front sampling end, thespacer recession defining two side openings, one on a first side of thetest sensor and another on a second side of the test sensor
 16. Thesensor of claim 15 wherein the two side openings are configured to allowa fluid to enter the fluid chamber through one of the two side openingswhen the first or second side of the test sensor is parallel to asurface that the fluid is on.
 17. The sensor of claim 1 wherein theconductive coating is formed from materials selected from the groupconsisting of carbon, metals and metal oxides.
 18. The sensor of claim 1wherein the three sampling wells are arranged to define an isoscelestriangle.
 19. The sensor of claim 1 wherein the first well forms one ofa reference electrode and a working electrode, and wherein the secondand third wells are each the other of the reference or working electrodefrom the first well.
 20. The sensor of claim 18 wherein the first wellforms one of a reference electrode and a working electrode, and whereinthe second and third wells are each the other of the reference orworking electrode from the first well.